Who buys a house that's 4.5x their salary?!
However, this presumes you will have 20-30 years of (more or less) uninterrupted prosperity which I think is unlikely.
People also do things like rent out a room or two to give themselves more of a cushion.
Here are some calculations using this site: http://www.mortgagecalculator.org/
I assumed a loan of 250k, 30 years, with no property tax or PMI since this is just for comparison.
Right now rates are ~3.5% so over 30 years you would pay $404k and $1122/month. Over the past 30 years the average interest rate has been 7.45% so over 30 years at that you would pay $626k and pay $1739/month.
So a very significant difference.
I did at one point rent a room from someone who was making $35k/yr who had just bought a $90k house and couldn't make the payment. It wasn't much cheaper than an apartment and the person made it clear almost every day that I was only welcome in the house because I paid more than half of his mortgage every month. He was an ass and I had no rental contract with him, so I left. His house got foreclosed upon a couple months later; I was going to buy it from the bank but he had trashed the entire inside and ripped out chunks of the exterior wall. Anyway, this was just a long winded story to say yeah, I can see what you're saying about renting a room to pay the mortgage. It would still make more financial sense to just buy a house you know you can afford.